Possible Light Flash from Black Hole Collision Spotted

When black holes collide, do they hide in the dark or emit flashes of light? That question is up the air after an Earth-based detector spotted gravitational waves, or ripples in the fabric of space-time, created by two black holes merging together. Previous work suggested that for black holes of this size — about 30 times the mass of the sun — there would be no bright flash, no hazy glow, no light to speak of.